1. The Field of the Invention
The present invention relates to a reclinable chair. In particular, although not exclusively, the invention relates to a synchro-tilt type chair in which the seat portion tilts rearwardly in synchronism with reclining action of the back portion. The invention is described primarily in the context of commercial office chairs. However, the invention is not limited in its application to commercial office chairs and may have application to any other type of seating such as public seating for theatres, aircraft or domestic seating.
2. The Relevant Technology
Reclining office chairs are well known. There are certain disadvantages associated with the conventional form of reclining office chair. One of the disadvantages is that as the occupant of the chair reclines rearwardly, his head drops in height. Therefore, the eye level of the chair's occupant will not be maintained constant. This may pose a difficulty if the occupant is working at a computer terminal where it is desirable to maintain a constant eye level relative to the screen. Additionally, in meetings it is also desirable to maintain a constant eye level relative to the other attendees of the meeting. Any person who undergoes a dip in eye level may effectively drop out of the conversation.
Another difficulty with conventional reclining chairs is that relative movement between the back portion and the seat portion may lead to frictional grabbing of occupant's shirt, thereby pulling out the occupant's shirt from his trousers.
U.S. Pat. No. 5,871,258 is in respect of a reclining office chair. The seat portion of the chair has a front portion connected to a rear portion by a resilient section in order that the rear portion carries most of the occupant's weight. The seat portion is operably connected to the reclining mechanism such that as the back portion reclines, the rear portion of the seat also tilts but additionally moves in a downward and forward motion. It will be appreciated that this further only serves to exacerbate the problem of tipping eye level. In this case, not only is the occupant's head dropping on account of their reclining action but also, the rear portion of the seat supporting the occupant's weight is also moving downwardly, with the practically certain result that the eye level of the occupant will dip during reclining action.
U.S. Pat. No. 5,314,237 raises the vertical height of the seat support during recline and thereby claims to achieve consistent vertical eye level. However, the chair disclosed in this US patent suffers from another shortcoming. As the seat portion lifts, the forward edge of the seat portion will accordingly be raised and thereby act as a hard edge bearing against the back of the occupant's knees. This can lead to circulatory problems for the occupant and/or lifting of the users feet from the floor with consequent poor posture.
Flexing of seat backs in the lumbar region of the user is also a desirable feature of modern office chairs. Chair occupants come in a wide range of different sizes and weights and it is therefore necessary for chair manufacturers to produce a chair which caters for a wide range of occupant sizes and weights. A larger, weightier person will be able to flex a chair back easily. On the otherhand, a person of light build may only be able to flex the back portion with a high degree of force. Accordingly, a person of light build may not receive much satisfaction from the feature of a flexible back portion.
Another common feature of reclinable chairs is the use of recline springs to resist rearward recline. Adjustment mechanisms are often provided to adjust the spring tension of the recline springs to suit the build of the occupant of the chair. Where such adjustment mechanism operate directly against the action of the spring, e.g., by way of a rotatable knob, generally a large number of turns of the knob are required in order to gradually stiffen the spring. Otherwise, the knob would be too stiff to turn in order to bring about the required adjustment.
It is therefore an object of the present invention to provide a chair which overcomes or at least addresses some of the foregoing disadvantages.